Over the swaying oceans and in the sun-soaked skies, there is more than enough energy to sail or fly around the world on light energy alone. Such endeavors are currently tricky and costly, but some developers are pushing the limits of technology as well as their own endurance to break air and water records.

With much of the planet mapped, photographed and digitized, these sailors and pilots believe the next frontiers lie in technology, in going farther, faster and cheaper and using less to do so. Like Charles Lindbergh crossing the Atlantic Ocean, they hope these feats will inspire the world to consider new ways to cut emissions while ushering in a new era for aviation and navigation, knowing that the technology and the desire are no longer limitations.

In May, the 31-meter MS Tûranor PlanetSolar completed its journey around the world, the first solar vehicle to do so and the largest solar boat ever built. The name Tûranor translates to "the power of the sun" and was inspired by the Elvish language in author J.R.R. Tolkien's mythology.

It traversed the oceans at a leisurely 5 knots while sipping electricity over 584 days, including a stop in Cancun, Mexico, for the 2010 U.N. climate talks. Navigators charted a course that avoided turbulent waters and harnessed as much of the ocean's currents as possible to gain a free boost.

The ship's slow pace made its catamaran hulls a convenient stop for passing birds and seals. It was also a ripe target for pirates in the Gulf of Aden, so crew members invited private security on board and festooned the boat with barbed wire to ensure safe passage.

The Tûranor PlanetSolar consumes 20 kilowatts on average and can generate up to 120 kilowatts of electricity, topping out at 10 knots. On the top deck, there are 38,000 solar cells spanning 537 square meters. It also carries 11 tons of lithium-ion cells that can charge fully in a day and give enough juice to sail for three days under clouds. Immo Ströher, a German investor, provided much of the funding for the €15 million German-built vessel, which was completed in 2010.

Wright Brothers with no gas
The PlanetSolar team is now preparing the ship for its next voyage, a 2013 scientific expedition to study the Gulf Stream, according to Rachel Bros de Puechredon, the communications head for Switzerland-based PlanetSolar SA. "The idea is that our boat is a great tool for scientific measurement because it does not emit anything," she said.

The preparations include design retrofits to apply some of the lessons the team learned. The partially submerged propellers, for example, did not achieve their advertised performance. "Theoretically, it should have had great efficiency, but it did not, so we are switching to a more conventional propeller," de Puechredon said.

Crews are also refitting the ship's cabins to accommodate scientists and their instruments. "These instruments will have to be optimized regarding the energy consumption," de Puechredon said, noting that there is little electricity to spare on a voyage, especially with a larger crew.

These solar energy challenges become more acute in the sky, but that has not deterred Bertrand Piccard and André Borschberg, Swiss pilots who plan to fly across the United States on sunlight alone next year. Piccard previously circled the planet in a balloon in 1999, and the gondola he used is on display at the Smithsonian National Air and Space Museum.

Borschberg and Piccard formed the Solar Impulse team to build a plane that could cross continents and lay the groundwork for one that could fly around the globe: the HB-SIA prototype.

The HB-SIA aircraft has a 208-meter wingspan, wider than the Boeing 787. It has four electric motor nacelles, weighs 3,527 pounds and flies at an average speed of 43 mph. Its lithium-polymer batteries make up a quarter of its weight. In the sky, the plane harvests sunlight using 11,628 solar cells covering 200 square meters on its wings and horizontal stabilizer. Solar Impulse invested €120 million over the past nine years in the project.

On average, each 10-horsepower motor only has 6 kW of electricity at its disposal, roughly the same as the Wright Brothers had on their first flight. Despite the plane's size, the pilot only has 1.3 cubic meters of space in the cockpit that can go from freezing to sweltering over the course of a flight.

Night flights
"The project was, of course, about building an aircraft, but it was more about saving energy," said Borschberg, speaking last week at the Swiss Embassy in Washington, D.C. "The power we can use is the power of a scooter."

The dynamics of flight make all these compromises necessary, but the HB-SIA has already posted some impressive results. The Solar Impulse team set a flight record with 26 hours, 10 minutes, 19 seconds aloft, spanning day and night. Next summer, they plan to fly from San Francisco to New York City with a stopover in Washington, D.C.

The team also wants to build a bigger plane that can fly for five to six days at a time. With this aircraft, Borschberg and Piccard will attempt to fly around the world in 2015, taking turns at the controls.

The PlanetSolar and Solar Impulse teams acknowledge that these feats do not translate directly into new paradigms and it may be some time before photovoltaic panels are commonly seen on wings and decks. "We do not believe that you can just put solar cells on a boat and it will work," de Puechredon said. However, with current technologies and these proofs of concept, "we don't need to wait another 15 years to fly around the world."

Piccard echoed this sentiment. "What is important is to show that we can go from the dream to reality," he said. He noted that the first gliders were made from cloth and wood, technology that was available to the Babylonians; all that was lacking was the will to make one. For that reason, when faced with the possibility of large-scale renewable transportation, Piccard said, "it would be crazy to answer 'yes' and stupid to answer 'no.'"